Cleanup: Remove unnecessary checks
Don't migrate buildversion on updatedb to PootleConfig

It won't work because the necessary tables are not yet present.
Also it is not necessary because this upgrade is already performed later
in the upgrade management command.
Recover ability to save buildversion using djblets

Since updatedb cannot rely on having the buildversions in PootleConfig
(see previous commit), we need to get back the legacy code to save the
buildversion using djblets.
Bugfix: Specify removed field instead of relying on model

Since we removed the description_html fields in b44dcf03 (in 2.5.1 and master)
we have to specify the fields instead of relying on the model, because they
do not longer exist there.
Styleguide: Use single quotes for template tags and filters in HTML attributes

So we avoid clashing with the HTML double quotes as much as possible.
Dev docs: Add guidelines on how to use migrations, upgrade and initdb
Cleanup: Provided build versions are always integers

So avoid the conversion.
commands: Fix a conditional UnboundLocalError
Security release: Update Django requirement to 1.5.6

https://www.djangoproject.com/weblog/2014/apr/21/security/